1. Field of the Invention
The present invention relates to a method of reducing kogation on the surface of a heater for applying thermal energy to an ink, an ink-jet recording process, an ink-jet recording apparatus, a recording unit, and a method for lengthening the life of an ink-jet recording head.
2. Related Background Art
Various systems have heretofore been proposed on printing using an ink-jet system. Among others, an ink-jet system (the so-called bubble-jet system) described in, for example, Japanese Patent Application Laid-Open No. 54-51837 or the like, in which an ink is ejected as ink droplets by the action of thermal energy, features that the formation of a high-density multi-nozzle in a recording head can be realized with very ease, high-quality images can be provided at high speed and very low cost, and printing can also be conducted on plain paper having no special coating layer. According to this system, a heater of a recording head is rapidly heated, thereby generating bubbles in a liquid on the heater to cause a rapid volumetric increase of the liquid. A droplet of the liquid is ejected from an nozzle of the recording head by the working force due to this rapid volumetric increase and applied to a recording medium, thereby conducting printing.
According to this system, however, a decomposition deposit (the so-called scorch) of an ink may be built up on the surface of the heater in some cases as the result that the heater of the recording head is repeatedly heated for ejecting the ink upon mass printing. In some cases, the build-up of the scorch may involve a problem that thermal energy cannot be effectively transferred from the heater to the ink, so that the quantity of the droplets ejected and the velocity of the droplets ejected are reduced compared with the initial printing, which adversely affects the quality of images formed. When it is intended to continuously achieve high-quality printing in this case, it is necessary to change the recording head. Such circumstances lead to increase in printing cost for users as a whole. Accordingly, achieving more reduction in kogation on the heater, which has a possibility of causing such circumstances, so as to more lengthen the life of the recording head is always an important technical problem to aim at a further improvement in the bubble-jet system.
For example, Japanese Patent Application Laid-Open No. 3-160070 has proposed an ink comprising an oxo anion. As examples of the oxo anion, are mentioned phosphates, polyphosphates, phosphoric esters, arsenates, molybdates, sulfates, sulfites and oxalates.
It is an object of the present invention to provide a method of reducing kogation on the surface of a heater for applying thermal energy to an ink in a recording head to eject the ink from the recording head.
Another object of the present invention is to provide an ink-jet recording apparatus which permits higher-quality printing and the achievement of a more lengthened life of a recording head.
A further object of the present invention is to provide a recording unit which permits high-quality printing over a long period of time.
A still further object of the present invention is to provide a method for lengthening the life of a recording head to achieve further reduction in printing cost while providing high-quality prints.
The above objects can be achieve by the present invention described below.
According to the present invention, there is thus provided a method of reducing kogation on the surface of the outermost protective layer of a heater for applying thermal energy to an ink to eject the ink from an orifice in an ink-jet printer having a recording head equipped with the heater, wherein the outermost protective layer comprises a metal and/or a metal oxide, and the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, xcex3-aldonolactone, xcex4-aldonolactone and aldonates.
According to this constitution, the kogation on the outermost protective layer of the heater can be extremely effectively reduced. The reason why such an effect is brought about by using such an ink is not clearly known. However, it is considered that at least one selected from the group consisting of aldonic acid, xcex3-aldonolactone, xcex4-aldonolactone and aldonates in the ink interacts with the metal and/or the metal oxide making up the outermost protective layer of the heater to prevent kogation or facilitate decomposition of scorch and separation of scorch from the heater surface.
When the metal contained in the outermost protective layer of the heater is tantalum, or the metal oxide is tantalum oxide, the effect becomes more noticeable. Supposing that the quantity of energy applied to the heater is Eop, and the threshold quantity of energy applied to the heater, which is required to eject the ink, is Eth, the kogation-preventing effect of the present invention becomes far excellent when the quantity of energy applied to the heater is preset in such a manner that Eop meets the relationship
1.10xe2x89xa6Eop/Ethxe2x89xa61.50.
According to the present invention, there is also provided an ink-jet recording process comprising the step of applying thermal energy to an ink to eject the ink from an orifice, wherein the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, xcex3-aldonolactone, xcex4-aldonolactone and aldonates.
According to the present invention, there is further provided an ink-jet recording apparatus comprising:
an ink container portion containing an ink,
an ink-jet recording head having a heater for applying thermal energy to the ink within an ink flow path, which is fed from the ink container portion, and
a means for applying a pulsed electric signal in response to recording information to the heater, wherein the heater has an outermost protective layer comprising a metal and/or a metal oxide, and the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, xcex3-aldonolactone, xcex4-aldonolactone and aldonates.
According to the present invention, there is still further provided a recording unit comprising an ink container portion containing an ink, and an ink-jet recording head for ejecting the ink from an orifice by the action of thermal energy, wherein the ink-jet recording head is equipped with a heater for applying thermal energy to the ink, which has an outermost protective layer comprising a metal and/or a metal oxide, and the ink comprises (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, xcex3-aldonolactone, xcex4-aldonolactone and aldonates.
According to the present invention, there is yet still further provided a method of lengthening the life of a recording head equipped with a heater for applying thermal energy to an ink, which is suitable for use in an ink-jet recording process comprising the step of applying thermal energy to an ink to eject the ink from an orifice, the method comprising providing an outermost protective layer comprising at least one of a metal and a metal oxide on the heater, and using, as the ink, an ink comprising (a) a coloring material, (b) a liquid medium, and (c) at least one selected from the group consisting of aldonic acid, xcex3-aldonolactone, xcex4-aldonolactone and aldonates.